2015-09-17_PERMIT FILE - C1984065A ‎(2)‎

• Permit No: C1984065A
• IBM Index Class Name: Permit File
• Doc Date: 9/17/2015
• Doc Name: pp.4-53 to 4-73
• Section_Exhibit Name: 4.4 Reclamation & 4.5 Post Mining Land Use
• Media Type: D
• Archive: Yes

Sediment Pond A Reclamation
Alternate Sediment Control
Sediment Log substitute for Silt Fences
The following table summarizes the peak water stage, trap efficiency and silt
fence length for the three reclaimed areas associated with Sediment Pond A
reclamation.
Description
Peak Water Stage
Feet
Feet
Trap Efficiency
%
Length
Feet
Area 1
0.06
83.74
400
Area 2
0.09
81.79
774
Area 3
0.06
82.59
26
The design flow rate for the silt fence is 10 gallons per minute per square foot.
The peak water stage for area 1 is 0.06 feet or 0.72".
The peak water stage for area 2 is 0.09 feet or 1.08".
The peak water stage for area 3 is 0.06 feet or 0.72".
The key factor in sediment control is the trap efficiency. According to data
published by American Excelsior Company, its 12" Curlex sediment log has a
trap efficiency (% Soil Retained) of 70.3% and a flow rate of 37.5 gallons per
minute per square foot. Its 6 and 9 inch sediment logs have a trap efficiency of
53.9% at 42.5 gallons per minute per square foot.
The high flow rates of the sediment logs in relation to the silt fence design would
indicate run-off will not overtop the sediment logs. The sediment logs will filter
the run-off faster than the sediment fences and not cause the water to back up
and flow around them, which frequently happens with sediment fence. In
addition, the design performed in SedCad demonstrates very little sediment loss
will occur after the site has been seeded, mulched and has a sediment log in
place. Therefore the lower trap efficiency of the sediment logs is not considered
significant.
Sediment logs (9") will be keyed into the natural soil at the low point of each
area as shown on page 4.58 -ix. The total length of the sediment logs will be
comparable to the length indicated in the approved silt fence designs including
tie back distances. The sediment logs will be overlapped to prevent flow bypass
when pieces are joined to achieve the appropriate total linear footage.
NCIG Coal Ridge No. 1 4-58vii 09115